Human herpesvirus 8 (HHV-8) has been etiologically linked to Kaposi sarcoma, multicentric Castleman's disease, and primary effusion lymphoma (PEL). The virus encodes a homolog of interluekin-6 (viral IL-6, vIL-6), and this viral cytokine has been implicated in development and pathogenesis of HHV-8 associated neoplasias. vIL-6 is required for PEL cell growth and survival, and it is known to localize to the endoplasmic reticulum (ER) of these cells where it is competent to mediate its pro-growth and survival effects. The mechanism by which vIL-6 mediates these activities in latently infected PEL cells is unclear. However, we have recently identified a novel interaction partner of vIL-6, vitamin K epoxide reductase complex subunit 1 variant 2 (VKORC1v2), which also localizes to the ER and functions to promote PEL cell growth and survival by a mechanism involving its interaction with vIL-6. In a yeast two-hybrid screen and subsequently by co-precipitation assay, VKORC1v2 was also shown to interact with thioredoxin-like protein 1 (TMX1), an ER-localized protein known to participate in the reduction of disulfide bonds. ER localization and interaction of VKORC1v2 with TMX1 suggest that these proteins may play a role in the folding of vIL-6 and/or in regulating the ER stress response. Recent studies have also indicated that the IL-6 signal transducer, gp130, is required for the growth and maintenance of PEL cells although the specific role of vIL-6 in this process has not been determined. This F31 application proposes to further characterize the vIL-6:VKORC1v2 interaction at the molecular level, to determine the connection of VKORC1v2 and TMX1 with vIL-6 activity, and to elucidate the contribution and mechanism of vIL-6:gp130 signaling to PEL cell growth and viability. By understanding the molecular mechanisms of vIL-6 effects in virus biology and pathogenesis, new targets may be identified and exploited for therapeutic benefit to treat PEL and other HHV-8 associated diseases.